The refrigeration systems with forced ventilation usually applied to refrigerators and freezers, generally use a compact evaporator of the tube-fin type comprising a plurality of fins incorporated to and trespassed by a set of tubes arranged in series in the form of a coil and carrying a refrigerant fluid. A forced airflow is forced to pass through the evaporator, which airflow is drawn from the inside of an environment to be cooled, in order to be refrigerated by the evaporator and discharged back to the interior of said environment, as it occurs for example in the refrigerating or freezing compartments of a refrigeration appliance.
These evaporators are constructed to assure a certain acceptable degree of thermal exchange between the forced airflow that is forced to pass over the tubes of the evaporator and over the fins orthogonally affixed to said tubes. However, since the heated air to be forced through the evaporator contains humidity in a higher or lower degree as a function of the operation to which the environment to be refrigerated is submitted, this humidity tends to condensate, causing the formation of ice in the evaporator.
The formation of ice occurs in a non-uniform way in the evaporator, with the ice accumulating more intensively on the leading edge of the fins and the tube, that is, at the region in which the airflow enters into the evaporator, restraining the airflow cross section between the fins.
Aiming at maintaining an adequate performance of the evaporator during the operation of the refrigeration system to which it is coupled, it is necessary to periodically remove, with a certain frequency, the ice accumulated in the evaporator. The defrost operations are usually automatically effected by the control system of the refrigeration appliance, generally a refrigerator, freezer, or a combined appliance with both functions.
The evaporators of the tube-fin type considered herein have been developed with the purpose of enhancing the heat transfer, increasing the thermal efficiency and allowing the use of more compact components of lower cost.
Following the evolutional process, the evaporator E had the fins 10 thereof modified, from a continuous form, as illustrated in FIG. 1 of the attached drawings, extending along the length of the evaporator according to the direction of the forced airflow path, to an interrupted form defined by fins that are mutually spaced, not only transversally to the direction of the forced airflow path, but also longitudinally along the length of the evaporator, as illustrated in FIG. 2 of the drawings, making the fins 10 be longitudinally arranged in rows that are transversal to the direction of the airflow path, with the fins 10 of each row being mutually parallel and spaced.
With the objective of imparting more capacity to the evaporator E to operate with the non-uniform pattern of ice formation, but allowing an operation that continues to comply with the requirements of thermal exchange efficiency, a constructive arrangement is usually employed, according to which the spacing between the fins 10 of the same row decreases from the first row of fins 10 provided close to the air inlet region of the evaporator E, to the last row of fins 10 provided close to the air outlet region of the evaporator, as illustrated in FIG. 2, which also shows, in a simple way, the non-uniform formation of ice G on the fins 10 and tubes 20 of the evaporator E. Nevertheless, the known decreasing variation of the spacing between the fins 10 of each row can, as a function of the distribution flexibility made possible, lead to different evaporator configurations, which are constructed either to increase the thermal exchange efficiency to the detriment of the capacity of the evaporator to operate with a certain degree of ice formation, or to increase said capacity to the detriment of the thermal efficiency of the evaporator E.
FIG. 3 of the enclosed drawings illustrates, schematically and partially, an arrangement of fins 10, in which the spacing therebetween has been calculated to increase the thermal exchange efficiency, to the detriment of the capacity to operatively support a certain degree of formation of ice G. The formation of ice G tends to prematurely obstruct the passage of the forced airflow through the evaporator.
FIG. 4, similarly to FIG. 3, illustrates an arrangement of fins 10, in which the spacing therebetween aimed at increasing the capacity of the evaporator to operate with the formation of ice G, to the detriment of the thermal exchange efficiency. The result of this arrangement is the provision of an evaporator that requires less frequent defrost operations, but which operates with low efficiency in terms of heat transfer.